Terminal connectors for power and signal wiring to industrial equipment come in many forms and provide a multitude of functions. One particular style of connector that has become popular particularly for wiring in environments subject to vibration employs a ‘screw-less type terminal with direct pressure’ (as defined in Annex D of IEC 60947_1:2004. “Low-voltage switch gear and control gear Part 1: general Rules and referred to herein as “screw-less type terminals”. Such terminals are often used to make permanent wiring connections to industrial equipment. Screw-less type terminals generally include a strong spring that maintains pressure on a conductor clamp in which the terminated conductor is securely retained. Screw-less type terminals may be “tool-less” or may require a tool such as a “hex” or “Allen” key or screwdriver to compress the spring, removing pressure from the conductor clamp and allowing insertion of a conductor into the terminal. Tool-less type terminals will often include a lever incorporated into the terminal body to compress the spring removing pressure on the conductor clamp.
In industrial situations it is sometimes necessary to disconnect a circuit while maintenance is performed on a piece of equipment. Sometimes switches are provided for the purpose of isolating equipment but there is always the possibility that a switch may be switched on while a worker is working on the connected circuit. This is often addresses by tagging the switch with a danger tag indicating that the circuit is being worked on. Switches may also be lockable but this is a more expensive solution which may not be justified where maintenance is infrequent.
Terminals may also be provided with test points that permit the insertion of a probe or plug for voltage measurement or, link with the link removed, a current meter may be connected in series. Removal of the link may also be used as a means of isolating the circuit for maintenance, but leaves the circuit prone to reconnection without warning if someone replaces the link.
Prior art disconnect terminals typically use a circular pin as the connection link. The pin fits into a small circular hole which is similar in size to a 4 mm test socket which is quite dangerous. If the circular pin is removed, it exposes the hole which is the same size as 4 mm test points located on either side of the link (i.e. 3×4 mm holes in a row). Therefore if the link is removed and a technician is working on the circuit, a second technician could in error insert a test lead plug into the centre hole by mistake and expose his workmate to supply voltage.